A robo's condition may lose its shine, acquire dirt, and thus become dirty. When a robo gets dirty, both its offensive and defensive capabilities suffer. All parts of a robo may become dirty.
It becomes dirty from one of several reasons: falling into magma in a holosseum stage, following use of the Soulboost, or simply frequent use of the robo. Also, the frequent use of charges will lead to a dirtier robo (Ray 01, Tricerion and Wolfen are the most affected by this).
Dirt can be cleaned off by using a cloth that is not dirty or purchasing a cleaning robo's services.